1. FIELD OF THE INVENTION
This invention relates to color television picture tube structures and to methods of manufacturing such structures.
2. DESCRIPTION OF THE PRIOR ART
Color television picture tubes comprise a viewing face or panel having a three color mosaic phosphor screen or image viewing portion of the faceplate, a color selection device in the form of a shadow mask having an apertured pattern aligned with the phosphor areas of the selected colors and with three electron guns for protecting separate electron beams through the mask at characteristic angles to activate the respective color phosphors on the screen. Color selection is achieved by selectively controlling the intensities of the electron beams. The spacing and alignment of the mask with respect to the gun and the mosaic phosphor screen must be established with precision and maintained throughout the fabrication and life of the tube. Slight rotational or longitudinal misalignment of the mask, screen and guns will result in degradation of the images developed and their color fidelity.
Heretofore color picture tubes have been manufactured in sections which are sealed together following necessary internal processing and subassembly. These sections include a viewing faceplate comprising a screen portion of substantially spherical curvature and an integral rim portion or skirt extending generally normal from the screen portion toward a funnel section and a neck of that funnel in which the electron gun assembly is mounted. Prior to assembly of the faceplate and funnel, the mosaic phosphor is formed on the internal surface of the screen portion and the color mask is mounted by fastening it to the rim portion. The rim portion is then sealed to the funnel and the electron gun assembly is mounted in the neck of the funnel. The tube is then sealed, evacuated and gettered.
In order to obtain the degree of precision in alignment of the mask and screen assemble, the customary practice has been to form the screen by photographic processes by exposure of photo-sensitive resists including the several phosphors through the mask. The phosphors for the three colors are applied in sequence by applying a coating to the inner face of the viewing screen, precisely mounting the mask, exposing the screen to light through a mask from a point corresponding to the position in the final assembled tube of the electron gun for the subject color, fixing the pattern of phosphors for that color and removing the unfixed phosphor containing material from the inner face of the viewing screen. The photographic process is repeated for each color component of the phosphor screen, and therefore, the mask is removed and remounted a number of times during the screen forming process. It is essential that the mask be positioned with respect to the faceplate in the same position for each photographic process and in the final assembly of the tube. Therefore the mounting arrangement for the mask must be sufficiently rigid and precise to define a unique mask position with respect to the screen. Further, the relationship of the screen and mask subassembly as mounted on the funnel to the electron guns in the neck of the funnel must also be established as a unique position axially, longitudinally and in a planar to axial or tilt relationship.
The manufacturing steps and apparatus involved in the production of color picture tubes require precision in the manufacture of the screen assembly, funnel, seal edges between the screen assembly and funnel, and the funnel neck. Variation is the surface of the glass of the viewing screen can result in unacceptable distortion. Thus rejection losses are high even in the initial glass forming of the parts. The addition of mounting elements for the mask to the rim of the screen assembly is highly critical and subject to production losses. The separable screen assembly and mask must be jigged with precision relative to the lighthouse, the light source for photographically generating the phosphor mosaic, on each sequence for developing a pattern of phosphors for a color. The seal of the screen assembly and mounted mask to the funnel is subject to the misalignments either initially or it subject to distortion during the thermal cycling of the parts, both of which must be avoided or limited to a narrow range of dimensional tolerances.
In accordance with the above, an object of this invention is to improve the structure of color television picture tubes.
Another object is to improve the optical quality of the viewing screen of color television picture tubes.
A third object is to increase the precision of alignment of the phosphor mosaic, mask and lighthouse and electron guns for color television picture tubes.
A further object is to simplify the manufacture of color television picture tubes.